Which of the three great branches of our government is, when you get right down to it, the very marrow of our democracy — its last, best hope, as Lincoln might say?

That’s easy: In theory, it’s the judiciary, in particular the U.S. Supreme Court, whose members are the true heirs of the Founding Fathers, their living embodiment as keepers of the Constitution.

Sure, the U.S. Senate — the “world’s greatest deliberative body,” where such weighty matters as nuclear treaties, impeachment trials, even the fates of Supreme Court nominees are decided — is important. But, alas, it does seem, at times, an assemblage of windbags. And the quality of the membership is, well, spotty.

The House of Representatives is important, too — it’s “the People’s House” — though some of its members lose sight of that when there’s special interest money around for the taking. We expect more of the presidency and mostly we get it. But the office, like Congress, is a political arm, subject to all the ills of what the founders called “faction,” or partisan politics, as we know it. The courts, especially the Supreme Court, was to be the one branch free of partisan politics, or certainly the appearance thereof.

And that’s held true for most of our history. But not at the moment, thanks chiefly to Justice Antonin Scalia and, to a lesser extent, Justice Clarence Thomas.

It’s one thing for a justice to espouse an ideological point of view, but quite another to seem to show a blatant political leaning, as Scalia did by agreeing to talk — behind closed doors, yet — with the House Republican tea party caucus. In doing so, he gave the back of his hand to the appearance of impartiality.

Scalia’s not just any member of the high court. He’s its star — its best and wittiest writer.

A singularly immodest guy for a justice, he courts controversy and regularly calls attention to himself with caustic criticisms of the reasoning of his fellow justices, sometimes even when he agrees with them. In case they miss a point, he sends them “Ninograms” supporting his position.

In short, Scalia, as its best-known member, personifies the current court for much of the public. And, in the opinion of Bruce Fein, a high justice department official in the Reagan administration, Scalia, in secretly meeting with tea party Republicans, “galloped beyond the farthest boundaries of judicial propriety.”

Thomas is less a public presence than Scalia. But, along with Scalia, he attended a political gathering sponsored by the ultraconservative Koch brothers, big corporate contributors to the GOP, even as a case that affected corporate political giving was before the Supreme Court. (The court eventually ruled in favor of unrestricted corporate political contributions, as the Koch brothers presumably wanted.)

But the appearance of politics in our federal courts goes beyond just Scalia and Thomas, and involves both parties. Four appellate court rulings on the Obama administration’s health insurance reform law make the case.

In two rulings, federal judges appointed by Republican presidents struck down the law, in whole or in part, as unconstitutional, while two other federal judges, named by Democratic presidents, upheld it. What’s going on here?

Whatever the merits of the legal reasoning behind these conflicting decisions, it’s hard to escape thinking there’s more than a little partisan politics involved.

And why not? The Supreme Court itself seemed to sanction partisanship with the decision in 2000 by its five-member GOP majority that gave the presidency to George W. Bush.

Consider the circumstances. The presidential election is essentially a state function, the outcome determined by the Electoral College vote in the states. In 2000, the outcome turned on one state, Florida. There, the Florida Supreme Court was in the process of overseeing a recount when the U.S. Supreme Court stepped in, suspended the recount, then ruled in Bush’s favor on — of all things — grounds that the time allowed for recount under Florida law had expired.

How’s that for a one-from-column-A, one-from-column-B decision — or, if you prefer, an unabashed exercise in “judicial activism.” (It didn’t help appearances that Al Gore won the national tally by more than a half-million votes.)

If something similar had occurred in a Third World election, we’d have cried “fraud” and called for international sanctions and a new election.

The effects of that dreadful decision resonate today. For what we have now — the stunning indifference by Scalia and Thomas to the need for at least the appearance of political impartiality — is the logical extension of their blatantly partisan ruling in Bush v. Gore. John Farmer is a Star-Ledger columnist. Have a comment?